1. Field of the Invention
The present invention generally relates to an optical waveguide sheet and a manufacturing method thereof, and more particularly to an optical waveguide sheet that has an auxiliary layer for preventing light transmitted through the waveguide sheet from leaking or being lost and a manufacturing method thereof.
2. Description of the Related Art
As shown in FIGS. 1 and 2, light A1 from a light emitting element 50 as a light emitting source is introduced into and is transmitted through a conventional optical waveguide sheet 30. Then, the light is reflected by a reflecting pattern 40 formed on a backside of the waveguide sheet, and finally the reflected light exits to the outside of the waveguide sheet.
If the light A1 is introduced from the light emitting element 50 into the waveguide sheet 30, the light A1 is transmitted within the waveguide sheet 30 by total reflection. When the transmitted light A1 arrives at upper and lower boundary surfaces of the waveguide sheet 30, the light A1 is reflected or exits depending on the incident angle θ2 of the light A1. That is, the light A1 exits the waveguide sheet 30 at a refracting angle θ4 when the incident angle θ2 is larger than a critical angle θ1 at which the light is reflected in parallel to the boundary surfaces, and the light A1 is reflected back into the waveguide sheet 30 at a reflecting angle θ3 when the incident angle θ2 is smaller than the critical angle θ1.
The light A1 is reflected back on or exits from the boundary surfaces according to the above reflecting principle. Therefore, the intensity of the light A1 is weaker the longer the light A1 travels within the waveguide sheet 30.
FIG. 3 illustrates reflection and loss behaviors of the light A1 traveling in a conventional waveguide sheet 30 adapted in a keypad assembly. The keypad assembly includes a keypad 20 with a plurality of keys 21 having a transparent mark 22, respectively, a light emitting element 50, such as a Light Emitting Diode (LED) or the like, for emitting light A1, and an optical waveguide sheet 30 having one or more reflecting patterns 40 for scattering light A1 transmitted from the light emitting element 50 to the keys 21.
When the light A1 emitted from the light emitting element 50 is introduced into the waveguide sheet 30, the light A1 is transmitted through the waveguide sheet 30, then meets with the reflecting patterns 40 formed on the backside of the waveguide sheet 30.
The light A1 is reflected towards the keypad 20 by the reflecting patterns 40, and then exits through the transparent marks 22 formed on the keys 21, wherein the transparent marks have shapes of corresponding numbers, characters, symbols, and the like.
However, a conventional waveguide sheet has problems where light introduced from a light emitting element into the waveguide sheet leaks or is lost at boundary surfaces of the waveguide sheet.
Accordingly, the intensity of the Light A1 is weaker the longer the light A1 is transmitted within the waveguide sheet 30. Also, brightness is further reduced as the light A1 is transmitted through a longer distance from the light emitting element.